Analyzer devices that make use of X-ray spectrometry are typically employed, for example, for analysis of the elemental composition of a bulk sample or for determination of a thickness and elemental composition of a coating on a bulk substrate. X-ray spectrometry is based on the physical principle of X-ray fluorescence (XRF). A non-limiting example in this regard is energy dispersive X-ray spectrometry (EDX), which is employed in the following as a non-limiting example of techniques that rely on XRF.
FIG. 1 schematically illustrates some components of an EDX device. When powered, an X-ray tube 1 emits primary X-radiation that is used to excite X-ray fluorescence in a sample 3 under study. The primary X-rays emitted from the X-ray tube 1 are considered as a primary X-ray beam 5 and it may be provided in the soft and/or ultra-soft X-radiation regime. During an analysis, a shutter 2 is opened in order to let a primary X-radiation pass towards the sample 3. Alternatively, the X-ray tube 1 is only powered during analysis of the sample 3 and de-powered otherwise. In some setups, a primary filter 4 is brought into the primary beam 5. The physical realization of a primary filter may be, for example, a metallic plate with a thickness in the range of a few micrometers to several hundred micrometers. The primary filter 4 may be applied to modify the spectral distribution of the primary X-radiation in order to improve spectral sensitivity of the analysis. In a typical EDX device the primary filter 4 is implemented either as single fixed filter assembly or as an adjustable electro-mechanical filter assembly that allows for switching between primary filters of different characteristics.
In order to have a well-defined analysed area of the sample surface, the primary X-ray beam 5 is typically (but not exclusively) collimated by passing it through a collimator 6, which is predominantly realized by an aperture of desired shape and size arranged in a metallic plate. Typical aperture shapes include, for example, circular or rectangular apertures. The implementation of the collimator 6 can be either a fixed single metallic aperture of predefined shape and size or an electro-mechanical assembly that allows for to switch between apertures of different size and/or shape. Finally, the collimated and filtered primary X-ray beam 5 irradiates the sample 3 and thereby interacts with the sample material. Irradiation of the sample 3 invokes secondary X-radiation 7 to be emitted from the sample 3, including secondary X-ray fluorescence.
An energy dispersive detector 8 is used to collect the secondary X-radiation 7 emitted from the sample 3 in the direction of the detector window of the energy dispersive detector 8. The detector 8 generates an electrical signal that is descriptive of the secondary X-radiation 7, which electrical signal is provided to a multi-channel analyser 9 for analysis therein. An analysis across multiple channels enables deriving a spectrum of the secondary X-radiation 7 emitted from the sample 3 in a solid angle spanned by the detector window. An EDX device may further include a video microscopy arrangement integrated therein for observing and aligning the analysed portion of a surface of the sample 3.
In various applications of XRF devices, such as intensity mapping of the sample surface, coating thickness analysis, samples with fine structures, etc.) it is often desirable to have a high lateral spatial resolution. With the typical setup described in the foregoing with references to FIG. 1, a sufficiently high lateral spatial resolution can only be realized by implementing the collimator 6 such that it has an aperture that is sufficiently small in size. In this regard, typical aperture sizes (e.g. a diameter of a circular aperture or a diagonal of a rectangular aperture) are in the range of a few ten micrometers to a few hundred micrometers. Consequently, XRF devices that employ an electro-mechanical collimator assembly that enables switching between apertures of different shapes and/or sizes require accurate positioning of a selected aperture with respect to the primary X-ray beam 5 such that the collimated primary X-ray beam is accurately guided to a desired measurement location on the surface of the sample 3. Typically, required positioning precision is in the order of a fraction of the size (e.g. diameter or diagonal) of the selected aperture.